1. Field of the Invention
The present invention relates to an air bag module for a passenger seat of an automobile, and more particularly to a dual-stage seat air bag module for a passenger seat capable of easily controlling and changing gas pressures to be provided into an air cushion, thereby implementing a miniaturization and a lightweight of the air bag module.
2. Description of the Related Art
In general, an automobile includes various types of passenger protecting apparatuses, for example, such as a seat belt and an air bag system.
As among these passenger-protecting apparatuses, particularly, the air bag system is used with the seat belt, and thereby it is prevented that when an automobile collision occurs, body members such as a head, a breast, knees, etc., of a passenger are hit and injured by constructions inside the automobile.
Such an air bag system is mostly mounted in a front seat of the automobile, and is generally distributed into a driver air-bag installed in a steering wheel and a passenger air-bag installed in a crash pad on or on the upper surface of a passenger glove box.
Because the air bag system should be operated momentarily and promptly when an accident such as the automobile collision occurs, various types of inflators are installed in the air bag system for the prompt expansion and spread of the air bag.
As representative inflators, there are an explosion-type inflator for inflating an air bag momentarily by generating gas by combustion or explosion of gas forming agent based on expansive materials, a gas charging type inflator for jetting compressed gas stored in a pressure vessel and inflating an air bag when an automobile collision occurs, and an hybrid type inflator combining advantages of the above-mentioned types of inflators.
FIG. 1a is an exploded perspective view showing a dual-stage air bag module which is generally installed in a front passenger seat of an automobile, and FIG. 1b is a cross-sectional view schematically showing a construction of an inflator shown in FIG. 1a. 
As shown in FIG. 1a, a conventional dual-stage air bag module for a passenger seat includes an air cushion 10, a cushion holder 20 for holding the air cushion 10, an inflator 30 for generating gas and providing it to the air cushion 10, and a housing 40 for receiving the inflator 30.
The air cushion 10 is received within the housing 40 with a folded state to have a required form. That is, to the inner lower portion of the air cushion 10 is coupled the cushion holder 20. This cushion holder 20 is again fixed to the housing 40.
The inflator 30 for providing gas to inflate the air cushion 10 is included in the housing 40.
The inflator 30 performs a gas feeding to the air cushion 10 in two steps. As shown in FIG. 1b, the inflator 30 consists of a first combustion chamber 34a and a second combustion chamber 34b separated from one another by an inner diaphragm 32.
In the first and second combustion chambers 34a and 34b are included a first igniter 36a and a second igniter 36b which are connected to gas forming agent (not shown) respectively.
Thus, responding to an electrical signal from a collision sensor (not shown), the first igniter 36a is ignited to burn gas forming agent, and thereby primary compressed gas is generated to fill the air cushion 10.
Then, after a predetermined time interval, the second igniter 36b is ignited to burn gas forming agent included therein, and secondary compressed gas is generated to secondarily fill the air cushion, thereby making a complete expansion of the air cushion 10.
However, because the conventional dual-stage air bag module for a passenger seat should make the two steps of gas output pressures using one inflator 30 and it is also designed to discharge only a desired gas output pressure respectively, there was a problem that control and change of the gas output pressure for obtaining a desired expansivity of the air cushion can not be performed easily.
In addition, there was a problem that size and weight of an air bag module are increased inevitably due to size and weight of the dual stage inflator.